Pokémon have always had the ability to evolve in order to become the next Pokémon in the chain and gain some significant strength. In this game, evolution does exist but it's not tied to progress of the Pokémon's level/CP, but rather based on an amount of candy that you obtain throughout the game. To get candy, you can do one of several things. First, catching a Pokémon of the species will give you 3 Candy outright. If you Transfer the Pokémon to Professor Willow, you will receive 1 Candy. Finally, when you hatch an egg, you will get between 5 and 30 candy. Candy isn't just used for evolution but also to power up Combat Points.

Evolution does power a Pokémon up, but you may wonder what happens to the Combat Points bar. While the points increase, the bar will stay level meaning that the Pokémon can still be powered up, depending on the level.

Before

After

Below is a list of all Pokémon, sorted by how many candies are required to evolve them.

As of the Johto update, Pokémon can now evolve using items, specifically the Metal Coat, King's Rock, Dragon Scale, Sun Stone and Up-grade. These are required in addition to candy requirements in order to evolve the Pokémon. They are obtained from Pokéstops.